This invention relates to a screening apparatus for macerating and screening a paper feedstock in a paper manufacturing process, and more particularly to a strainer suitable for use in a pulper for macerating a paper feedstock or the like.
In general, a pulper for paper making or the like includes a strainer for screening a paper feedstock of good quality macerated through a rotor rotating.
A strainer which has been conventionally used for this purpose is generally constructed as shown in FIG. 1. More particularly, a conventional strainer which is generally designated by reference numeral 100 in FIG. 1 includes a flat straining body or plate 102 formed into a disc-like shape and provided with a number of through-holes or apertures 104 functioning as straining apertures. The strainer 100 also includes a plurality of cutters 106 mounted on an upper surface of the straining plate 102 using fixing means 108 such as bolts or the like in a manner to be perpendicular to a direction of rotation of a rotor (not shown) arranged so as to rotate in proximity to the strainer 100. The strainer 100 thus constructed permits its maceration ability to be enhanced by cooperation of the cutters 106 with the rotor rotating.
Unfortunately, the conventional strainer constructed as described above has a lot of disadvantages.
One of the disadvantages encountered with the conventional strainer is that the cutters 106 account for a considerable part of the surface area of the straining plate 102, resulting in an area of distribution of the straining apertures 104 on the straining plate 102 being reduced.
Another disadvantage of the prior art is that the cutters 106 are arranged on the upper surface of the straining plate 102 in a manner to project therefrom, to thereby cause a gap between the rotor and the straining plate 102 to be increased, so that a screening effect exhibited by the straining apertures 104 of the straining plate 102 due to vortex resulting from rotation of the rotor may be reduced.
A further disadvantage of the prior art is that the length of a cutting edge formed at each of the cutters 106 is restricted.
Also, the conventional strainer has still another disadvantage that there is a possibility of causing the fixing means 108 such as bolts or the like for fixing the cutters 106 on the straining plate 102 to be loosened during the screening operation, leading,to removal of the cutters 106 from the straining plate 102.
In addition, the conventional strainer causes the number of parts required for forming the strainer 100 to be increased.
Yet another disadvantage encountered with the conventional strainer is that the manufacturing is highly troublesome and time-consuming because it is required to manufacture the individual cutters 106 and mount them on the straining plate 102 by means of bolts or the like.